Chop the greens, and pick out discolored or tough bits.

Place the greens in a sink full of water. Swish them around to wash them, then carefully lift them out, to leave any grit or dirt behind. If the water is dirty, repeat the process.

Drain the greens in a collander or strainer, until almost dry.

Heat oil in a saute pan or fry pan. Add the onion, stir, and saute until softened.

Add the greens to the pan. Using tongs, stir them around to bring them all in contact with the hot oil, and let them start to cook down. (Greens may be added in two or more steps, if needed.)

Toss them again every few minutes, bring the more cooked greens on the bottom to the top, until cooked to taste.